Map Projection for Small Areas

I am working in small areas like 100x100 meters for a school assingment. I want to use a plain cartesian coordinate system and also, I want the unit distance 1 meter (distance between X=0 and X=1) in order to use measurement tool. I guess these kind of projection
can't be selected.

When I don't select any map projection in code, "Invalid or Missing Projection" pop-up appears and ask me to select a projection type whenever I start my application. If I choose unmodified coordinates I can get what I want, but I don't want to
do it everytime. I am studying electronics and not familiar with geographical sciences, so I don't know how to set geographical properties. I will appreciate if I can find any solution to this problem.